The present invention relates to tractor-trailer fifth wheel coupling devices in general and is particularly directed to a removable king pin support assembly for these devices.
Tractor-trailer operators are required to use fifth wheel king pins manufactured to meet industry standards. Recommended practice is to utilize one size king pin for conventional commercial applications and another size for heavy duty off-highway operation or in hauling heavy loads. Because of this, manufacturers offer trailer king pin support assemblies which will accommodate either size king pin. Also, because the exposed end of the king pin is subject to wear or damage as a result of constant coupling and uncoupling, it is most advantageous to vehicle owners and operators to have a king pin which can be easily and quickly replaced. Interchangeability of equipment therefore is of major concern and importance to a vehicle operator or fleet owner.
Known devices have achieved the desired result by providing a king pin support in the form of separable housings which cooperate to rigidly secure the king pin to the underside of the trailer. While stability and ease of removal are prime factors to be considered in fifth wheel applications, it is also essential that the king pin be properly located and rigidly held so that it does not rotate relative to the supporting parts. Improper location or looseness in the assembly will contribute to early failure and, accordingly, short life of the assembly.
Removable king pin supports fall into two basic categories, those in which the separable parts permit the king pin to be inserted and removed from within the trailer and those permitting insertion and removal from the trailer underside. The latter type has proven to be most acceptable for a number of reasons, the most obvious being that the former type, when encountering a loaded trailer, requires partial or full unloading for access to the king pin assembly.
Proper location and stability is achieved in known devices by employing cooperating tapered surfaces on mating separable housings to provide a tight wedging action. This permits the king pin to be self-centered and thereby securely retains and locates the king pin in assembled relation. Ordinarily, two or more housing members are provided with mating tapered surfaces and, when assembled, provide a tight frictional connection between the members. In certain instances, in addition to the housing members, the king pin itself is formed with a tapered surface. A disadvantage in structures of this type is that special machining is required to insure that the tapered surfaces always come in tight, solid engagement when assembled. A further disadvantage is that it is difficult to break such a connection. The desirable self-centering feature created by the tapered configuration is outweighed by the difficulty encountered in breaking the tight fit and by the machining costs.
King pins may be designed for removal in a number of ways. For example, one common design includes a socket in the king pin bottom for receiving a conventional socket wrench and a threaded king pin upper end adapted to be connected to one of the separable housings. In this design the threaded king pin portion is an actual load carrying member in the assembly and, due to the severe impact loads it is subjected to, is readily susceptible to damage and early failure.
Means are also provided in known devices to prevent king pin rotation when in service. Some require considerable modification to the king pin itself and to at least one of the housing members in order to function properly. Others require separate spring loaded locking members for engaging slots formed in the king pin. In the latter case, a separate locking member is required and further an additional operation is necessary to retract it when the king pin is being removed.
While the above devices operate in a satisfactory manner, because each requires considerable structural modifications to be made to the king pin and at least one of the support members and/or the addition of another operating member to effect the locking action, they are costly and structurally complex.